1. Field of the Invention
This invention relates generally to improvements in check valves, and more particularly, but not by way of limitation, to fluid flow-actuated check valves for use in float collars or float shoes in well cementing operations.
2. Description of the Prior Art
The prior art contains a number of teachings of flow control check valves for use in floating equipment employed in the cementing of casing in oil wells. It is normally desirable to maintain the check valves in an open condition in the float shoes or float collars of the casing as the casing is being run into the well so that the casing can automatically fill from the bottom at a predetermined rate in order to save costly rig time which would otherwise be expended in manually filling the casing string from the surface as it is being run into the borehole. Currently available tool designs for such floating equipment are limited by some form of sacrificial mechanical part for maintaining the check valve in an open position such as shear plates, shear pins, extrusion rings, tension collars or the like. Such mechanical items must have a calculated strength such that the check valve is held open until a predetermined amount of pressure differential or a predetermined fluid flow rate acts upon the tool. The reliability of such prior art designs depends upon whether or not the materials being deformed or sheared perform in the predicted manner. If the materials do not perform in the predicted manner, the check valve member may either be released prematurely or may not be released at all. The elimination of sacrificial mechanical devices would be a distinct advantage.
It should also be noted that the currently available tool designs for automatically filling float shoes or float collars provide no means for reopening and reclosing the check valve employed therein after the deformation or shearing of the sacrificial mechanical part previously maintaining such check valve in an open position. This structural limitation in the prior art devices eliminates the possibility of testing the check valve mechanism for operability when in position down hole prior to commencing the actual cementing operation.
Those forms of automatic filling float shoes or float collars which require a ball or plug to be dropped through the casing string to seal in the valve mechanism of the float shoe or float collar to seal off the valve mechanism so that pressure can be applied thereto to release the locked open check valve through shearing or deformation of a sacrificial mechanical part are characterized by a disadvantageous time delay during which the ball or plug must fall through the fluid in the casing. Prior art mechanisms of this type are illustrated at pages 2412 and 2413 of the Halliburton Services Sales and Service Catalog No. 37.
It will be clearly seen that all forms of prior art tool designs discussed above prevent the possibility of reverse circulation through the check valve mechanism once release of the check valve has been obtained through shearing or extruding the sacrificial mechanical part previously maintaining the check valve in an open position.
U.S. Pat. Nos. 3,776,250 and 3,385,372, each granted to Lloyd C. Knox, and U.S. Pat. No. 3,385,370, granted to Lloyd C. Knox, et al., all of which are assigned to Halliburton Company, the assignee of the present invention, disclose various forms of prior art flow control valve structures employing frangible pins and otherwise deformable elements. A non-indexing automatic fill-up valve utilizing shear pins is shown on pages 2414 and 2415 of Halliburton Services Sales and Service Catalog No. 37.